Turbulent flow electrodialysis cell

ABSTRACT

There is disclosed a two-chambered electrocell comprising one or a plurality of anode chambers, a crude flow inlet and a crude flow outlet communicating with the anode chamber, one or a plurality of cathode chambers, and a catholyte outlet communicating with the cathode chamber, wherein cylindrical anodes are located in the anode chamber, wherein the anode chamber is defined by a membrane having a first side and a second side, wherein the first side of the membrane communicates with crude fluid circulating within the anode chamber, and wherein the second side of the membrane is supported by a plurality of support members, wherein a pressure of crude fluid in the anode chamber deflects the membrane between the support members toward the cathode to form a crude flow path having a constantly changing direction, and wherein the cathode chamber is defined by the second side of the membrane and the two-chambered electrocell, and the support members and a cathode are located in the cathode chamber.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a two chambered electrocell, a threechambered electrocell and a multiple chambered electrodialysis cellhaving a crude flow configuration with a constantly changing directionto cause turbulence at a membrane surface. The crude flow configurationis caused by deflection of the membrane around a plurality of parallelsupport members.

BACKGROUND OF THE INVENTION

Membrane electrocells (ECs) are used primarily by the chlor-alkaliindustry and for sea water desalination. Commercially available devicesare made in a flat configuration with stack designs similar to that offilter presses. An EC, in its simplest form, is made up of an anode, oneor more membranes, and a cathode. The membrane sheets are sealed so thatfluid chambers are formed in layers between the electrodes. ECs arecapable of separating chemicals because the membranes containmicroscopic pores which allow chemical species to diffuse from onechamber to another. Such diffusion is slow. However charged species(ions) can be pulled through the pores more quickly if an electricalfield is applied between the electrodes. For example, in a two-chamberedcell (one membrane), if a sodium sulfate solution is fed into an anodechamber, an electric field will cause sodium ions to move through themembrane into a cathode chamber. This migration will produce a sulfuricacid solution in the anode chamber and a sodium hydroxide solution inthe cathode chamber. The efficiency of this scheme is enhanced withmembranes which specifically allow ions of a specified charge to pass.Therefore, in this example, a membrane would be used which selectivelypasses positive ions. This would inhibit movement of hydroxide ions fromthe cathode chamber into the anode chamber, thus saving electricalenergy.

Commercial ECs are generally either electrodialysis cells orsalt-splitting cells. Electrodialysis cells are made up of a largenumber of membranes stacked between two electrodes. In these systems,the membranes alternate between cationic (passes cations) and anionic(passes anions) types. The chambers are filled alternately with a saltbrine and a water solution to be desalted. Salts are pushed by theelectric field from the water into the brine to produce a desalinatedstream.

Salt-splitting cells (chlor-alkali cells) differ from electrodialysiscells primarily because their output is a base stream, an acid stream,or a generated gas instead of a purified water and a brine stream. Mostsalt splitting cells use only one or two membranes per cell, and largescale production is achieved by stacking many cells together.

Recent attempts to improve ECs have tried to increase turbulence.Turbulence has been increased by installing grids or "turbulencepromoters." These turbulence promoters fill a gap between an electrodeand a membrane so that fluid must flow around a series of obstructions.This causes a high degree of mixing which can break up boundary layersat membrane surfaces and remove bubbles which can occlude parts of theelectrode. Usually the main advantage of turbulence promoters is animprovement in electrical efficiency. Potential drawbacks to turbulencepromoters are that they foul easily and cause significant pressuredrops. Fouling can be overcome by pretreating feed chemicals andpressure drops can be overcome by limiting the EC dimension. However,both solutions to fouling and pressure drops add considerable expense tothe cost of an EC system.

One example of a cell designed to limit pressure drops while maintainingturbulence in the DEM® cell from electrocatalytic. In this cell, theelectrodes are "dished out" over the active surface so that the flowpath in its headers is relatively unrestricted. This avoids many of theflow distribution problems often found in narrow gap cells. Pressuredrops can also be minimized in a lantern blade cell. The "lantern blade"term refers to an electrode made up of slats arranged in parallel and atan angle in a "Venetian blind" pattern. The membrane is supported by theedges of the pieces, and fluid flows in the gap in the slats.

ECs are used to produce materials which can also be obtained by othertechnologies. Therefore, economic considerations are of paramountconcern in the design of ECs. Further, the greatest expense iselectricity consumption. To minimize electrical resistance andelectricity use, EC cells are usually designed with fluid compartmentsas thin as possible. For example, in ICI's two-chambered, lantern-bladeelectrocell (model FM21), the gap between electrodes is 2.5 mm. However,one drawback to narrow gap distances is that they limit fluid velocitiesthrough the EC (typically <10 cm/sec). This exaggerates foulingproblems.

Fouling problems are often not a major concern in commercial saltsplitting applications because the feed streams can be pretreated tominimize fouling. However, pretreatment of feed streams addsconsiderably to expenses. Moreover, there are uncommercializedapplications for ECs where fouling prevents commercial viability. Theseapplications include processing streams which contain either suspendedparticulates or large gel-forming molecules in solution. Examples ofsuch uncommercialized applications include desalting of liquid foods,removal of lignin from black liquor in wood pulp processing anddesalting of pharmaceutical process streams.

The most rapid type of fouling is a surface phenomena. During ECoperation, particles or large molecules in solution can adhere to theelectrode and membrane surfaces due to electrical forces or due todifferences in surface energies between the fluids and the surfaces.Eventually an impermeable film is formed over the surfaces. A method ofsuppressing this build up is to increase the amount of turbulence in thefluid. High sheer generated by turbulence can pull foulants away fromthe surface before they adhere to a surface and make a firm attachment.Therefore there is a need in the art for an EC which could maximizeturbulence while maintaining small electrode spacing for processingfouling fluids.

High levels of turbulence can also increase the limiting current of anEC. "Limiting current" refers to a situation where ion flux throughmembranes is so fast that the concentration of ions near one side of amembrane becomes depleted. When this happens, the voltage gradient inthe fluid near the membrane grows so steep that water begins to splitinto H⁺ and OH⁻. Such splitting consumes electrical energy withoutimproving cell performance. Turbulence is, therefore, beneficial becauseit can delay the onset of water splitting by increasing mixing in thefluids and wiping away the ion-depleted layer. Other benefits ofturbulence in ECs include the fact that bubbles that form on electrodesare stripped away quickly. Also minimizing ion depletion conditions nearthe membrane reduces voltage drops in the cell and lowers energyconsumption.

Accordingly, there is a need in the art to find an alternate solution tomembrane fouling problems that can allow the use of feedstock materialshaving a high suspended solids content, such as black liquor in the pulpand paper industry. The present invention was made to address theseissues.

SUMMARY OF THE INVENTION

The present invention provides an electrodialysis cell having a fluidflow design with high turbulence at a membrane surface by having a flowpath with a continual change in flow direction. The present inventioncan take the form of a two chambered electrocell, a three chamberedelectrocell or a multiple chambered electrodialysis cell.

For a two-chambered electrocell, the present invention provides atwo-chambered electrocell having one or a plurality of anode chambersand one or a plurality of cathode chambers within the electrocell,comprising: (a) an enclosed electrocell having a crude flow inlet and acrude flow outlet communicating with an anode chamber and a catholyteinlet and a catholyte outlet communicating with a cathode chamber: (b)an anode chamber within the enclosed electrocell comprising cylindricalanodes arranged in parallel within the anode chamber, wherein the anodechamber is defined by a membrane having a first side and a second side,wherein the first side of the membrane communicates with crude fluidcirculating within the anode chamber, and wherein the second side of themembrane is supported by a plurality of support members arranged inparallel to each other and to the anodes, wherein a pressure of crudefluid in the anode chamber deflects the membrane between the supportmembers toward the cathode to form a crude flow path having a constantlychanging direction; and (c) a cathode chamber within the electrocell anddefined by the second side of the membrane, the cathode, and theenclosed electrocell, and comprising the support members and a cathode.Preferably, the catholyte flow in a direction perpendicular to the crudeflow direction.

In a three chambered configuration, the present invention provides athree-chambered electrocell having one or a plurality of anode chambers,one or a plurality of crude chambers, and one or a plurality of cathodechambers within the electrocell, comprising: (a) an enclosed electrocellhaving an anodelyte flow inlet and an anodelyte flow outletcommunicating with the anode chamber, a crude flow inlet and a crudeflow outlet communicating with the crude chamber, and a catholyte inletand a catholyte outlet communicating with the cathode chamber; (b) ananode chamber within the electrocell defined by an anode, a plurality ofanode support members arranged in parallel, and an anode membrane havinga first side and a second side, wherein the first side of the anodemembrane communicates with crude flow circulating within the crudechamber and the second side of the anode membrane communicates with theanode chamber and with the anode support members, wherein a greaterpressure applied to the crude chamber results in the anode membranebeing deflected toward the support members within the anode chamber; (c)a cathode chamber within the electrocell defined by a cathode, aplurality of cathode support members arranged in parallel to each otherand to the anode support members, and a cathode membrane having a firstside and a second side, wherein the first side of the cathode membranecommunicates with crude flowing within the crude chamber and the secondside of the cathode membrane is supported be the plurality of cathodesupport members, wherein a greater pressure applied to the crude chamberresults in the cathode membrane being deflected toward the cathode; and(d) a crude chamber within the electrocell defined by the first side ofthe anode membrane and the first side of the cathode membrane, whereinthe anode support members and the cathode support members are offsetfrom each other such that a crude flow path with a constantly changingdirection is formed upon application of a greater pressure to the crudechamber than to the anode chamber or the cathode chamber. Preferably,the catholyte flow in a direction perpendicular to the crude flowdirection.

In an electrodialysis configuration, the present invention provides amultiple-chambered electrodialysis cell having an anode chamber, aplurality of brine chambers, a plurality of desalinate chambers, and acathode chamber within the electrodialysis cell, comprising: (a) anenclosed electrodialysis cell having an anodelyte flow inlet and ananodelyte flow outlet communicating with the anode chamber, a pluralityof brine chambers, a plurality of desalinate flow chambers, wherein eachbrine and desalinate flow chambers comprise an inlet and an outlet, anda cathode chamber having a catholyte inlet and a catholyte outlet; (b)an anode chamber within the electrocell having an anode, and an anodemembrane wherein the anode membrane has a first side and a second side,wherein the first side of the anode membrane communicates with a fluid(anodelyte) within the anode chamber and the second side of the anodemembrane communicates with a brine chamber: (c) a plurality of brinechambers, each defined by a series of support members arranged inparallel and each defined by one or two brine membranes, wherein thebrine chamber adjacent to the anode chamber is defined by the secondside of the anode membrane and a first side of a brine membrane, orwherein a brine chamber not adjacent to the anode chamber is defined bytwo brine membranes wherein the first and the second brine membraneshave a first side and a second side, wherein the first sides of thebrine membranes communicate with the brine chamber and the second sidesof the brine membranes communicate with an adjacent desalinate flowchamber, wherein greater pressure applied to a fluid in the desalinateflow chamber or the anode chamber causes each brine membrane or anodemembrane to deflect in a direction of the brine chamber, and wherein thesupport members of adjacent brine chambers are offset: (d) a pluralityof desalinate chambers, each defined by the second side of the brinechamber membranes, wherein the desalinate chamber adjacent to thecathode chamber is defined by the second side of a brine membrane and asecond side of a cathode membrane, and wherein a desalinate chamber notadjacent to the cathode chamber is defined by the second sides of brinemembranes from adjacent brine chambers; and (e) a cathode chambercomprising a cathode, a series support members arranged in parallel andoffset from the adjacent brine chamber, and a cathode membrane having afirst side and a second side, wherein the first side of the cathodemembrane communicates with the cathode chamber and the second side ofthe cathode membrane communicates with an adjacent desalinate flowchamber, such that greater fluid pressure applied to the adjacentdesalinate flow chamber than the cathode chamber deflects the cathodemembrane toward the cathode chamber support members. Preferably, thecatholyte, anodelyte and brine flow in a direction parallel to eachother and the desalinate flows in a direction perpendicular to thecatholyte, anodelyte and brine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a small portion of a cell of a two chambered electrocellwherein the anodes are 1.3 cm diameter cylindrical members (solid orhollow) located in the anode chamber, the support members are about 0.6cm diameter rods located in the cathode chamber, the spacing betweenanode centers is around 2.0 cm, and the minimum gap distance between theanode and cathode is around 0.6 cm to maximize efficiency of theelectrocell. The distance between support members is from 1.8 cm to 3.0cm. The flow pattern is in a cross-flow design wherein the feedstock(i.e., "crude") flows through the gap between the cylindrical anodes andthe membrane according to the thick arrow. The continually changing flowdirection of the crude induces a high amount of turbulence at the firstside of the membrane. The catholyte flows perpendicular to the crude (inFIG. 1, this is out of the page). Induced turbulence for the catholyteis less than the crude because the flow path is straighter.

FIG. 2 shows a small portion of a three chambered electrocell having aflat structure and alternating anodes and cathodes and havingcylindrical (coming into and out of the page) and offset support membersthat create a crude flow path with a constantly changing direction whenpressure is applied to deflect each of the membranes.

FIG. 3 shows an a small portion of a multiple chambered electrodialysiscell having a flat anode, an adjacent anode chamber, a plurality ofbrine chambers, each having a series of parallel support members in anoblong shape with rounded faces in contact with each membrane surfaceand that are offset in adjacent brine chambers, a plurality ofdesalinate flow chambers that show a constantly changing direction forfluid flow that is formed when pressure is applied to deflect eachmembrane around the support members, and a cathode chamber having a flatcathode and a series of cylindrical and parallel support members thatare offset from the support members in an adjacent brine chamber.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an electrocell having a novel design forpromoting high turbulence in that portion of the electrocells sensitiveto fouling or limiting current problems. The inventive electrodialysiscell designs allow for electrochemical processing of fluids which wouldfoul surfaces in conventional electrocells and allow for higher currentdensities in electrodialysis. Applications of the inventiveelectrodialysis cells include, for example, salt splitting of industrialwaste to reclaim and recycle needed chemicals, adjustment of pH ofchemical solutions by cation removal, production of NaOH from mineraldeposits, precipitation of species from solution by cation removal, suchas precipitation of lignin from black liquor by sodium removal, removalof sodium from foods, desalination of sea water, and electrosynthesis oforganic molecules.

The inventive electrochemical cell enables processing of fouling streamsmore easily than other electrocells due to its unique geometry. In allthree electrocell configurations, the membranes (e.g., anode membrane,brine membranes and cathode membranes) are intentionally allowed todeflect in response to fluid pressure differentials so that a flow pathwith a constantly changing direction is formed. Such changes indirection create high degrees of turbulence due to inertial effects.Instilling turbulence by virtue of a constantly changing direction ispreferable to using turbulence promoters because no grid is placedwithin the flow path. A grid, by nature, will create numerous pockets ofstagnant flow which will foul. Another advantage ofdirectionally-induced turbulence of the present invention, is that fluidshear is concentrated at membrane surfaces where it is most beneficial.This reduces pressure drops through the cell in comparison with cellswith turbulence promoters.

Two-Chambered Electrocell

In the two-chambered configuration, the cathodes are made from plates ofstainless steel or another suitable material that is electricallyconductive and non-corrosible. Cathodes may be laminated with a moreelectrically conductive material in their center to improve powerdistribution characteristics. Anodes are preferably cylindrical and maybe hollow or solid. A conductive core of a material different than theanode surface may be used to improve power distribution. Anode diametersizes in a cylindrical configuration range from about 0.5 cm to about 5cm.

The membranes in the two chambered configuration are semipermeablemembranes and are supported by a plurality of support members arrangedin parallel within a cathode chamber. A higher fluid pressure applied tothe fluid in the crude chamber will cause the membrane to deflect towardthe cathode, forming a membrane geometry which, in cross section,resembles that made by support cables of a suspension bridge.Preferably, the support members are made from a non-corrosive substance.such as a rigid polymer, and the surfaces of the support members incontact with the membrane should be smooth and rounded to avoid physicaldamage to the membrane. The distance between support members should begreater than the diameter of the anode but less than the anode diameterplus 3 cm. That portion of the support member in contact with themembrane, when the support member is in a rod or elongated rod-likeconfiguration, should be between one-fourth and three-fourths the anodediameter from the cathode surface.

The anode chamber is shown in cross section in FIG. 1. The cylindricalanodes are arranged in parallel such that the axes of the anodes forms aplane perpendicular to the page and horizontal across FIG. 1.Preferably, the anodes are about 0.5 cm to about 5 cm diameter cylinderswith the spacing between anode cylindrical centers from about 0.75 cm toabout 5 cm, and preferably about 2 cm. Once there is pressure applied tothe crude feedstock (as depicted in FIG. 1) the semipermeable membranes,supported by the supporting members in the cathode chamber, form aserpentine flow path as shown in FIG. 1. Due to the continually changingdirection of the fluid flow, there is a high degree of turbulence formedalong the boundary layer along the first side of the semipermeablemembrane.

A crude flow path with a continually changing direction is formed bycreating a cell containing two cathodes with their surfaces facing eachother. The distance between cathodes should be approximately 1 cm toabout 2 cm greater than the anode diameter. Membranes and membranesupports are installed such that the support members are directlyopposite each other, as shown in FIG. 1, and are offset from thecylindrical anodes as seen in FIG. 1. Preferably, cylindrical anodes arefixed within the crude chamber in the center of gaps formed betweenmembrane supports. A crude flow perpendicular to the anodes (the anodescome out of the page in FIG. 1) is induced in the crude chamber, withthe result that the crude fluid must wind its way through a serpentinepath defined by the membranes and the anodes.

Common Features of Each Electrocell Configuration

The semipermeable membrane must sag to achieve a continually changingflow path for the crude. The semipermeable membrane is allowed todeflect up to a predetermined distance beyond the supporting member.Desired membrane deflection is caused when a sufficient amount oftransmembrane pressure of from about 1.0 psig to about 25 psig isapplied to the fluids (i.e., crude and catholyte) on both sides of themembrane.

The high amount of turbulence at the first side of the semipermeablemembrane helps to prevent surface fouling at the first side of themembrane. Surface fouling and internal membrane fouling both degradeperformance of electrodialysis cells. Internal fouling is usually aresult of an equilibrium driven chemical precipitation in thesemipermeable membrane pores. Such precipitation is particularly seriousbecause it leads to irreversible stretching of pores within the membraneand permanently degraded current efficiencies. Such precipitation couldoccur because of changes in pH as cations are drawn from an acidic crudeto the basic catholyte. In order to minimize this problem, it isimportant to moderate the pH of the catholyte and to keep the flow rateof the catholyte high enough to avoid concentration polarization at thesecond side of the membrane, or to perform the electrolytic process atlower current densities, or maximize membrane area, and/or increasefluid temperatures to surpass equilibrium point. For some forms ofprecipitation, particularly sulfate precipitation, the presence of anelectrical field inhibits precipitation. To take advantage of thisphenomena, the electrodialysis cell must be designed to avoid regions oflow field strength in the membranes.

An advantage of the inventive electrocell designs is that it is not assensitive to drying induced rupture as conventional designs due to ahigh amount of slack in each membrane in each of the three electrocelland electrodialysis cell designs. During drying, membranes tend toshrink, and in conventional cells, this can lead to membrane rupture. Inview of the fact that the membrane in the inventive electrochemicalcells are not stretched taught, shrinking can be accommodated bydecreased deflection between the support members.

Conventional electrochemical or chlor-alkali cells operate with fluidscontaining 1500 to 300,000 mg/L dissolved solids and must be virtuallyfree of suspended solids (no more than 1.0 NTU turbidity). Therefore,conventional electrochemical and chlor-alkali cells will have their feedstreams pretreated with filtration equipment, ion exchange resin,sequestion agents to keep salts in solution, and/or with acid additionfor pH control in order to eliminate salt precipitation within the EC.This eliminates possible deposition of suspended solids on the surfaceof the membrane. The inventive cells have a turbulent flow design with acontinually changing flow direction while maximizing membrane contacttime as the fluid comes into direct contact with the deflectedsemipermeable membrane in the "serpentine" fluid path. This turbulencein inventive ECs maintains a stirring effect which maintains suspendedparticles in solution and reduces the amount of settling material on themembrane surface to minimize fouling. Moreover, pretreatment proceduresare generally unnecessary with the inventive EC, thus saving operatingand capital costs.

The limiting electrical current allowed in an EC is inverselyproportional to the thickness of the unstirred boundary layer on thefirst side of the membrane. Increased turbulence afforded by the designof the inventive ECs allows electrodialysis operations at highercurrents than conventional electrocells or chlor-alkali cells. Higherlimiting current densities are a result of higher rates of mass transferwithin the anode chamber and because the turbulence of the inventiveflow path design provides a thinner or no unmixed laminar boundary layeron the first side of the membrane. Therefore, inventive ECs may beoperated at higher current densities than conventional ECs orchlor-alkali cells. For example, in water desalination procedures withconventional ECs or chlor-alkali cells, the operating current is usuallykept just below the limiting current density of the cell instead of at amore economically favorable higher current density. The inventive EC canperform water desalination procedures at higher current densities todesalinate water more economically. This also reduces capital andoperating costs for equipment and for a procedure utilizing theinventive electrocells and electrodialysis cells. Most importantly, withthe present inventive design, smaller electrocells would be needed thatcould significantly reduce capital costs.

As current density is increased toward its limiting current, voltagepotential increases up to a point where water may split into hydrogenand hydroxyl ions. The hydroxyl ions can form precipitates with calcium,magnesium or other cations and foul the membrane first surface. In theinventive EC designs, water splitting can occur only at higher currentdensities because the limiting current is higher. This advantage of theinventive cell designs allow for water desalination operations of cellsat higher current densities with less salt precipitation problems. Thisreduces capital costs of the equipment. Further, voltage drops are lowerfor the inventive cell than for conventional cells when compared withwater desalination operations at similar current densities and whenoperating near each cell's limiting current. This reduces operatingcosts for the inventive EC.

In any of the inventive electrocell configurations, the cathodes aremade from plates of stainless steel or another suitable, noncorrosivematerial. Cathodes may also be laminated with a more conductive materialto improve power distribution characteristics. Anodes are preferablycylindrical in design in the two-chambered electrocell and in a plateshape in the three-chambered electrocell and the electrodialysis cell,and may be hollow or solid. A conductive core of the anode made from amaterial different than the material comprising the anode surface may beused to improve power distribution. Anode diameters in a cylindricalconfiguration range from about 0.5 cm to about 5.0 cm.

Since the catholyte is a non-fouling fluid, it is not necessary toinstall a catholyte flow path with a continuously changing direction inthe cathode chamber in any of the three inventive configurations.Catholyte flow is, preferably, parallel to the support members throughchannels defined by the cathode, the support members and the membrane inany of the three inventive configurations.

In the two-chambered electrocell, the three-chambered electrocell andthe electrodialysis cell, the membranes are semipermeable membranes of amonofilm or a bifilm design. Preferably, the semipermeable membrane isrelatively thin (e.g., from about 1 mil to about 10 mils). Suitablemembranes include, for example, Nafion® membranes from the 100, 400 and900 series, Desal #N100, and RAI-Pall #R1030. In selecting asemipermeable membrane, it is important to consider if the membrane ispliable enough to be deflected by fluid pressure differences and to beable to conform to a path around rounded support members.

Three-Chambered Electrocell

In a three-chambered electrocell (e.g., salt-splitting cell), thepotentially fouling feedstock is introduced into a crude chamber in theelectrocell between the anode and cathode chambers. In thisconfiguration, the electrodes (i.e., anodes and cathodes) are preferablyflat and made from appropriate conductive and non-corrosive materials(e.g., stainless steel, precious metal oxide coated titanium) and theymay be laminated with more conductive materials to improve powerdistribution. Membrane support members are installed in both the anodechamber and the cathode chamber. The support members are similar to thesupport members in the two-chambered electrocell, and preferably rodshaped. The support members in the anode and cathode chambers are offsetfrom each other, such that when the crude chamber is pressurized, a flowpath with a continually changing direction is formed within the crudechamber. Preferably, the electrodes are from about 0.5 cm to about 2.0cm apart and the support members (diameter or similar distance) spanabout one half of the electrode gap. Spacing between support members(i.e., the distance between outer walls of support members) is fromabout 1 cm to about 3 cm. The semipermeable membranes are subject to thesame constraints as in the two-chambered electrocell configuration,however, the membrane communicating with the cathode chamber ispreferably of the cationic type while the membrane communicating withthe anode chamber is preferably of the neutral or anionic type.

Electrodialysis Cell

In the electrodialysis cell configuration, the desalinate fluid (fluidto be desalted) flows through a plurality of desalinate flow chamberslocated parallel to and between an anode chamber and a cathode chamber.The flow path in the desalinate flow chambers is of the sameconfiguration (i.e., continually changing flow direction) as the crudechamber of the three-chambered electrocell. Between each of thedesalinate flow chambers is a brine chamber comprising the deflectedmembranes and support members (see, for example, FIG. 3). Preferably,brine flows parallel to the support members (i.e., into and out of thepage in FIG. 3) and perpendicular to the desalinate flow.

Preferably, in the electrodialysis cell, the membranes in the cellalternate between cationic and anionic (or neutral) types. As a result,current passing through the cell will be carried by cations through thecationic membrane, and carried by anions traveling in the oppositedirection through an anionic (or neutral) membrane. Since the membranetypes are preferably installed in an alternating pattern, this willcause ions to leave the desalinate fluid and become concentrated in thebrine chambers. It is important to instill turbulence in the desalinatechambers because ion depletion can lead to low limiting currents,accordingly, in the multiple chambered electrodialysis cell design, thedesalinate flow chamber is designed with a continually changing flowdirection. The flow path in the brine chambers does not induceturbulence, however, the ion concentration in the brine is high enoughthat limiting currents on the brine side of the membranes are notapproached.

It should be noted that in a preferred electrodialysis cellconfiguration, the salt solution in the anode and cathode chambers doesnot mix with either the brine or desalinate fluids. The anodelyte andcatholyte comes from a common reservoir, and after passing through theelectrodialysis cell, are recombined. This maintains a constant saltconcentration in the fluid.

What is claimed is:
 1. A two-chambered electrocell comprising one or aplurality of anode chambers, a crude flow inlet and a crude flow outletcommunicating with the anode chamber, one or a plurality of cathodechambers, and a catholyte outlet communicating with the cathode chamber,wherein cylindrical anodes are located in the anode chamber, wherein theanode chamber is defined by a membrane having a first side and a secondside, wherein the first side of the membrane communicates with crudefluid circulating within the anode chamber, and wherein the second sideof the membrane is supported by a plurality of support members, whereina pressure of crude fluid in the anode chamber deflects the membranebetween the support members toward the cathode to form a crude flow pathhaving a constantly changing direction, and wherein the cathode chamberis defined by the second side of the membrane and the two-chamberedelectrocell, and the support members and a cathode are located in thecathode chamber.
 2. The two-chambered electrocell of claim 1, whereinthe catholyte flows in a direction perpendicular to the crude flowdirection.
 3. The two-chambered electrocell of claim 1 wherein thesupport members have a center-to-center spacing greater than thediameter of the anode but less than the anode diameter plus 2 cm.
 4. Athree-chambered electrocell comprising one or a plurality of anodechambers having an anolyte flow inlet and an anolyte flow outletcommunicating with the anode chamber, one or a plurality of crudechambers having a crude flow inlet and a crude flow outlet communicatingwith the crude chamber, and one or a plurality of cathode chambers,wherein an anode and a plurality of anode support members are located inthe anode chamber, wherein the anode chamber is defined by an anodemembrane having a first side and a second side, wherein the first sideof the anode membrane communicates with crude flow circulating withinthe crude chamber and the second side of the anode membrane communicateswith the anode chamber and with the anode support members, wherein agreater pressure applied to the crude chamber results in the anodemembrane being deflected toward the anode support members, wherein acathode and a plurality of cathode support members are located in thecathode chamber, and the cathode chamber is defined by a cathodemembrane having a first side and a second side, wherein the first sideof the cathode membrane communicates with crude flowing within the crudechamber and the second side of the cathode membrane is supported be theplurality of cathode support members, wherein a greater pressure appliedto the crude chamber results in the cathode membrane being deflectedtoward the cathode, and wherein the crude chamber is defined by thefirst side of the anode membrane and the first side of the cathodemembrane, wherein the anode support members and the cathode supportmembers are offset from each other such that a crude flow path with aconstantly changing direction is formed upon application of a greaterpressure to the crude chamber than to the anode chamber or the cathodechamber.
 5. The three chambered electrocell of claim 4, wherein thecatholyte flows in a direction perpendicular to the crude flowdirection.